Previous in vitro studies on polymorphonuclear neutrophil (PMN) phagocytosis and killing of Pasteurella multocida have demonstrated a novel group of organisms that are resistant to PMN killing despite significant levels of cell association. Our overall objectives are identify the mechanisms of resistance of these strains to destruction by rabbit PMN and to isolate bacterial components that inhibit neutrophil activity. Specifically, we propose to determine whether cell-associated resistant bacteria are ingested by PMN using an assay of 14C-uridine uptake by pasteurella organisms in which phagocytized bacteria are prevented from incorporating uridine because it is excluded by PMN. If resistant strains are not ingested then we will examine aspects of the phatocytic process including opsonization with C3 and PMN degranulation. If however, resistant strains are ingested then we will examine their susceptibilities to several PMN bactericidal mechanisms including PMN generated H2O2, O2-, and lysosomal cationic proteins. Irrespective of the specific effect detected, we will attempt to characterize and isolate bacterial components associated with the resistance of these strains to PMN killing. The role of bacterial cell surface components in resistance to PMN activity will be assessed by treating resistant bacteria with a variety of enzymes including pronase, lipase, mixed glycosidases, hyaluronidase and neuraminidase. Treated bacteria will then be tested for their ability to resist killing by PMN. Capsular and cell wall extracts will be prepared and tested for their ability to inhibit PMN killing of susceptible P. multocida. Molecular weight fractions of inhibitory extracts will be prepared by ultrafiltration and each tested for PMN inhibitory activity. Inhibitory fractions will be analyzed for protein and carbohydrate content. Proteins will be further separated using native or SDS gel electrophoresis. Proteins thus identified will be recovered from the gel and tested for antiphagocyte activity. If cell surface components do not inhibit PMN function then concentrated culture filtrates will be evaluated for the presence of extracellular antiphagocyte factors. Molecular weight fractions will be prepared by ultrafiltration and each tested for PMN inhibitory activity. Inhibitory fractions will be analyzed for protein and carbohydrate content and proteins in inhibitory fractions will be separated using gel electrophoresis.